Mobile devices, such as mobile phones, notebook, computers, etc., typically have the ability to estimate their location and/or position using any one of several technologies such as, for example, satellite positioning systems (SPSs)—e.g., GPS, Galileo, Glonass and the like, advanced forward link trilateration (AFLT), Observed Time Difference Of Arrival (OTDOA), Cell ID or Enhanced Cell ID (ECID). Location or position estimation techniques typically involve the processing of measurements which may be based on signals acquired at a mobile device receiver. For example, a mobile device may acquire SPS signals or pilot signals transmitted from a terrestrial base station. Various measured characteristics of the acquired signals such as phase, signal strength, time of arrival, and/or round trip delay may be used in computing a position fix.
In a particular implementation, User Plane (UP) positioning such as SUPL (Secure User Plane Location) as set forth by the Open Mobile Alliance (OMA) is a framework within which location estimates obtained at a mobile device (e.g. a SUPL Enabled Terminal (SET)) or at a separate location server (e.g. SUPL Location Platform (SLP)) may be made available to other entities as part of a location service. Making these location estimates available to other entities (e.g. an external client such as a SUPL Agent) may be useful in particular applications such as, for example, providing emergency services, locating a user on behalf of another client user, obtaining driving directions or finding a nearby gas station, hotel, airport or hospital. Additionally, in certain instances a mobile device may also communicate with an SLP to obtain positioning assistance data such as, for example, a rough location, accurate time reference, data to assist in acquisition of SPS or terrestrial radio signals, local indoor navigation assistance data, SPS ephemeris data to assist in computing a location from SPS measurements. A location estimate may be referred to as a location, estimated location, position or position estimate—these terms being used synonymously herein.
In the case that an external SUPL Agent needs the location of a SET, the SUPL Agent would typically send a location request to the Home SLP (H-SLP) for the SET which would then instigate a SUPL session with the SET to obtain the SET's location after which the H-SLP would return the obtained location to the SUPL Agent. When a SET (SUPL enabled terminal) such as a mobile device is not served either by the home network or by a network with properties known to the SET's H-SLP (home SUPL location platform), however, it may not be possible for the H-SLP to obtain an accurate location for the SET or for the SET to obtain its own location accurately by engaging in a SUPL (Secure User Plane Location) session with the H-SLP.